So I was using the /locate command to find a nether fortress bounding box at -688, ~, -400 to get blaze rods but as I was bridging there I stumbled across the nether mainland. I then installed the "Basic Skyblock" mod from modrinth which should stop new chunks from generating, but for some reason the nether kept generating new chunks as I flew above it in creative mode with the mod installed. So, I have a couple question . 1.Are there any good mods for stopping block and mob generation while keeping bounding box generation? 2. How do I delete the delete chunks that I have already created?

 

And by the way this is on the singleplayer skyblock 2.1 world, and I am playing in 1.21.4

 

The easiest way would be to just install a datapack that prevents the generation of new chunks (ie, a skyblock datapack). You then put this folder in \your world\datapacks\<here>. Finding one that does that is the hard part.

There's also google-able solutions on how to prevent new chunks from generating such as editing level.dat, the world in MCEdit, etc etc.